The present invention relates to a process for producing an adhesive-treated polyester fiber cord useful as a reinforcing cord for a power-transmission belt. More particularly, the present invention relates to a process for producing an adhesive-treated polyester fiber cord which is suitable as a core cord of a lapped V belt and has an excellent handling property in a belt-forming procedure, an excellent adhesion to non-vulcanized rubber used in a belt-forming procedure, and a superior bonding property to a matrix rubber after vulcanization of the rubber, and exhibits an excellent adhesive durability to such an extent that even when the cord is brought into contact with water vapor during the vulcanizing procedure, the adhesive property of the cord is not degrated, and a superior belt-forming property.
A polyester fiber cord generally has excellent mechanical strength, modulus of elasticity, dimensional stability and heat resistance, and thus is useful as an excellent reinforcing cord for rubber-composite materials, for example, tires, belts and hoses which are employed under severe conditions, and thus the use of the polyester fiber cord is expected to increase.
Generally, the reinforcing fibers for rubber-composite materials, for example, belts, are employed in the form of a twisted yarn cord. The important properties for the cord are a high adhesive property of the cord to matrix rubber, a high mechanical strength of cord, a good balance between elongation under load and dry heat shrinkage of the cord, an appropriate heat shrinkage stress, and a superior adhesion of the cord to the non-vulcanized rubber in a forming procedure. For example, in the case of a belt, among the above-mentioned properties, the adhesive property and the mechanical strength of the cord significantly contribute to enhancing the load resistance and durability of the resultant belt, and the balance between the elongation under load and the dry heat shrinkage influences the dimensional change, (for example, the length) of the belt during movement of the belt, and closely relates to a power transmission efficiency of the belt. Further, the adhesion of the belt to the non-vulcanized rubber in a belt-forming procedure is a property special to the belt-forming procedure and closely relates to peeling or separation of the cord from the non-vulcanized rubber subjected to the belt-forming procedure and directly influences the yield of the product. Therefore, an adhesion process technology which enables the resultant product to exhibit well balanced properties, as mentioned above, is desired.
With respect to an adhesion of a polyester fiber cord with a rubber matrix, various types of resorcinol-formaldehyde latex adhesives (RFr adhesives) are provided by, for example, Japanese Unexamined Patent Publications No. 57-187,238 and No. 60-110,980 and Japanese Examined Patent Publication No. 8-2,971. When these adhesives are employed, the adhesion performance of the polyester fiber cord as a reinforcing fiber cord for power transmission belt is certainly sufficient, but the adhesives are disadvantageous in that the adhesion of the cord with the non-vulcanized rubber in the belt-forming procedure is insufficient and peeling or separation of the cord from the rubber matrix frequently occurs. Therefore, in the present stage, the close adhesion of the cord with the non-vulcanized rubber in the belt-forming procedure is ensured by coating a rubber adhesive prepared by dissolving an adhesive rubber in a solvent and in a small amount, on a periphery of a cord coated with an RFr adhesive.
However, the above-mentioned rubber adhesive causes the working environment for the belt-forming procedure to be bad and sticking of the non-dried rubber adhesive to a worker""s body is unhealthy. Also, the treatment with the solvent-containing rubber adhesive is disadvantageous in that the waste liquid-treatment cost is high and the working environment is bad, in comparison with the aqueous treatment.
The present invention was made, against the above-mentioned background, to provide a process for producing an adhesive-treated polyester fiber cord having excellent handling property and adhesion of the cord to non-vulcanized vulcanized rubber in a forming procedure, and a superior bonding property of the cord with a matrix rubber, and useful for rubber composite materials, particularly a power-transmission belt, having a high durability.
The process for producing an adhesive-treated polyester fiber cord of the present invention comprises:
subjecting a non-twisted or twisted polyester fiber cord to a first adhesive-treating procedure in which a first adhesive liquid comprising a polyepoxide compound and a blocked polyisocyanate compound in a solid weight ratio of 1/3 to 1/5 is applied to the polyester fiber cord and the first adhesive liquid-applied polyester fiber cord is heat treated at a temperature of 160 to 240xc2x0 C.;
twisting, where the polyester fiber cord has no twist, the non-twisted polyester fiber cord;
subjecting the first adhesive-treated polyester fiber cord to a second adhesive-treating procedure in which a second adhesive liquid comprising a resorcinol-formaldehyde condensation product resin and a rubber latex in an effective component weight ratio of 1/3 to 1/15, is applied to the first adhesive-treated polyester fiber cord, and the second adhesive liquid-applied polyester fiber cord is heat-treated at a temperature of 180 to 240xc2x0C.; and
subjecting the second adhesive-treated polyester fiber cord to a third adhesive-treating procedure in which a third adhesive liquid comprising an aqueous dispersion of a resorcinol-formaldehyde condensation product component (RF) in a molar ratio (R/F) of resorcinol (R) to formaldehyde (F) of 1/0.6 to 1/1.0 and a rubber component (G) containing natural rubber (NR) in a content of at least 15% by weight based on the total weight of the rubber component (G), in a solid weight ratio (RF/G) of the resorcinol-formaldehyde condensation product component (RF) to the rubber component (G) of 1/10 to 1/20 is applied to the second adhesive-treated polyester fiber cord, and the third adhesive liquid-applied polyester fiber cord is heat-treated at a temperature of 140 to 170xc2x0 C.
In the process for producing an adhesive-treated polyester fiber cord of the present invention, preferably, the polyester fibers in the polyester fiber cord are fibers treated with an epoxy compound during a fiber-forming procedure.
In the process for producing an adhesive-treated polyester fiber cord of the present invention, the polyepoxide compound contained in the first adhesive liquid is preferably selected from glycidyl ether compounds of polyhydric alcohol compounds.
In the process for producing an adhesive-treated polyester fiber cord of the present invention, the polyepoxide compound in the first adhesive liquid preferably has an epoxy group content of 0.2 equivalent or more per 100 g of the polyepoxide compound.
In the process for producing an adhesive-treated polyester fiber cord of the present invention, the blocked polyisocyanate compound is preferably selected from addition reaction products of a polyisocyanate compound with a blocking agent comprising at least one member selected from oxime compounds, phenol compounds and caprolactam.
In the process for producing an adhesive-treated polyester fiber cord of the present invention, the first adhesive-treated polyester fiber cord preferably has the first adhesive in a total solid weight of 0.5 to 1.5% by weight based on the polyester fiber cord.
In the process for producing an adhesive-treated polyester fiber cord of the present invention, the heat treatment for the first adhesive liquid-applied polyester fiber cord is preferably carried out under a stretched condition under which the first adhesive liquid-applied polyester fiber cord is elongated at an elongation of 2.0 to 4.5%.
In the process for producing an adhesive-treated polyester fiber cord of the present invention, the rubber latex contained in the second adhesive liquid preferably comprises, as a main rubber component, a vinylpyridine-styrene-butadiene copolymer rubber.
In the process for producing an adhesive-treated polyester fiber cord of the present invention, the second adhesive liquid optionally further comprises a blocked isocyanate compound in a weight ratio of 1/10 to 1/3 to the solid weight of the rubber latex contained in the second adhesive liquid.
In the process for producing an adhesive-treated polyester fiber cord of the present invention, the second adhesive-treated polyester fiber cord preferably has the second adhesive in a total solid weight of 2.0 to 3.0% based on the weight of the polyester fiber cord.
In the process for producing an adhesive-treated polyester fiber cord of the present invention, the heat treatment for the second adhesive liquid-applied polyester fiber cord is preferably carried out under a relaxed condition under which the second adhesive liquid-applied polyester fiber cord is allowed to shrink at a shrinkage of 0.5 to 1.5%.
In the process for producing an adhesive-treated polyester fiber cord of the present invention, the rubber component (G) contained in the third adhesive liquid preferably comprises natural rubber (NR) and a vinylpyridine-styrene-butadiene copolymer rubber (VpR) in a solid weight ratio (NR/VpR) of 2/8 to 4/6.
In the process for producing an adhesive-treated polyester fiber cord of the present invention, the third adhesive liquid optionally further comprises an aqueous dispersion of carbon black (C) in an effective component weight ratio (C/(RF+G)) of the carbon black (C) to the total of the resorcinol-formaldehyde condensation product component (RF) and the rubber component (G) of 1/3 to 1/10.
In the process for producing an adhesive-treated polyester fiber cord of the present invention, the third adhesive-treated polyester fiber cord preferably has the third adhesive in a total solid weight of 0.5 to 1.5% based on the weight of the polyester fiber cord.
The polyester fibers usable for the adhesive-treated polyester fiber cord of the present invention are preferably formed from a polyester having repeating units substantially consisting of ethylene terephthalate groups. The polyester fibers usable for the present invention may be formed from polyesters other than the polyethylene terephthalate, for example copolyesters of polyethylene terephthalate with a small amount of a third component, for example, isophthalic acid, 5-sodium sulfoisophthalic acid, adipic acid, tetramethylene glycol and diethylene glycol. The polyester fibers usable for the present invention include epoxy-pretreated polyester fibers prepared by treating polyester fibers with an epoxy compound.
In the process of the present invention, a non-twisted or twisted polyester fiber cord is subjected to the first, second and third adhesion procedures which will be explained in detail hereinafter. The twisted and non-twisted polyester fiber cord may be prepared by a conventional cord-forming method. For example, in the preparation of a twisted polyester fiber cord, a desired number of polyester fiber yarns are set parallel to each other, the parallel yarn bundle is first-twisted with a desired first twist number, a desired number of the first-twisted yarns are set parallel to each other and subjected to a final twisting with a desired final twist number, to form a twisted polyester fiber cord (a material cord). The first twist number is usually smaller than the final twist number, and the twisting direction of the first twist is opposite to that of the final twist.
In the process of the present invention, the twisted or non-twisted polyester cord (material cord) is subjected to a first adhesive-treating procedure with a first adhesive liquid. The first adhesive liquid for the first adhesion procedure comprises a polyepoxide compound (Ep) and a blocked polyisocyanate compound (Iso) in a solid weight ratio (Ep/Iso) of 1/3 to 1/5. The polyepoxide compound (Ep) preferably has two or more epoxy groups per molecule. The first adhesive liquid is in the state of an aqueous dispersion of the polyepoxide compound (Ep) and the blocked polyisocyanate compound (Iso). If the solid weight ratio (Ep/Iso) falls outside of the above-mentioned range, the resultant adhesive-treated polyester fiber cord exhibits an unsatisfactory adhesive property and an insufficient resistance to fatigue, namely durability.
The polyepoxide compound (Ep) usable for the first adhesion procedure preferably has a epoxy group content of 0.2 equivalent or more per 100 g of the polyepoxide compound (Ep). Also, the polyepoxide compound (Ep) is preferably selected from polyglycidyl ether compounds of polyhydric aliphatic alcohol compounds, which exhibit an excellent performance for the first adhesion procedure. The polyepoxide compound is usually employed in the form of an aqueous solution, emulsion or dispersion. The aqueous emulsion is prepared by dissolving the polyepoxide compound (Ep) in a small amount of a solvent, and emulsifying the polyepoxide compound solution in water by using a conventional emulsifying agent, for example, sodium alkylbenzenesulfonate or sodium dioctylsulfosuccinate. When the polyepoxide compound (Ep) is soluble in water, an aqueous solution thereof is employed. The polyepoxide compound (Ep) may be used together with a curing reaction catalyst, for example, an amine compound or imidazol compound.
The blocked polyisocyante compound (Iso) for the first adhesive-treating procedure is preferably selected from addition reaction products of a polyisocyanate compound, for example, diphenyl-methanediisocyanate or tolylenediisocyanate with a blocking agent comprising at least one member selected from oxime compounds, phenol compounds and caprolactam.
The blocked polyisocyanate compound (Iso) is usually in the form of fine solid particles and is employed in the state of an aqueous dispersion prepared by using a dispersing agent, for example, sodium dioctylsulfosuccinate.
The first adhesive liquid for the process of the present invention may contain an optional component other than the polyepoxide compound (Ep) and the blocked polyisocyanate compound unless the optional component hinders the purpose of the present invention. However, the first adhesive liquid is preferably free from rubber latex.
In the first adhesive-treating procedure, the amount of the first adhesive liquid adhered on the polyester fiber cord is preferably 0.5 to 1.5%, more preferably 0.8 to 1.4%, by weight, in terms of dry solid weight, based on the weight of the polyester fiber cord. If the adhesion amount of the first adhesive liquid falls outside of the above-mentioned range, the resultant adhesive-treated polyester fiber cord may exhibit an unsatisfactory adhesive property and a poor resistance to fatigue.
There is no limitation to the method of applying the first adhesive liquid to the polyester fiber cord. Usually, an immersion method is applied. The first adhesive liquid is adhered to the polyester fiber cord by the immersion method and, preferably, the first adhesive liquid-applied polyester fiber cord is dried at a temperature of 130 to 160xc2x0 C. for 60 to 150 seconds and then heat-treated at a temperature of 160 to 240xc2x0 C., more preferably 210 to 235xc2x0 C. for 60 to 180 seconds, more preferably 90 to 150 seconds. The drying and heat-treating procedure is preferably carried out under a stretched condition under which the first adhesive liquid applied polyester fiber cord is elongated at an elongation of 2.0 to 4.5%, more preferably 3.0 to 4.0%, still more preferably about 3.5%, to enhance the mechanical strength of the cord.
When the cord has no twist, the non-twisted, first adhesive-treated polyester fiber cord is twisted in the similar manner to that mentioned above.
The first adhesive-treated polyester fiber cord is subjected to a second adhesive-treating procedure in which a second adhesive liquid comprising a resorcinol-formaldehyde condensation product resin (RFr ) and a rubber latex (L) in an effective component weight ratio (RFr/L) of 1/3 to 1/15, preferably 1/5 to 1/12, is applied to the first adhesive-treated polyester fiber cord, and the second adhesive liquid-applied polyester fiber cord is heat-treated at a temperature of 180 to 240xc2x0C. A mixture of the resorcinol-formaldehyde condensation product resin (RFr) with the rubber latex (L) is referred to as an RFL adhesive, hereinafter. The RFL adhesive may be selected from conventional RFL adhesives for rubber material treatments. Preferably, in the RFL adhesive, the molar ratio of resorcinol to formaldehyde is 1/0.1 to 1/6, more preferably 1/0.5 to 1/4. When the effective component weight ratio (RFr/L) is less than 1/15, the resultant second adhesive liquid exhibits an insufficient agglomerating force and thus an unsatisfactory adhesive performance. If the ratio (RFr/L) is more than 1/3, the resultant adhesive-treated polyester fiber cord exhibits too high a stiffness and an unsatisfactory mechanical strength and an insufficient fatigue resistance.
There is no limitation to the type of the rubber latex (L). Usually, vinyl pyridine-styrene-butadiene copolymer latices are preferably employed as a main rubber component of the rubber latex (L). The second adhesive liquid optionally comprises, as a cross-linking agent, a blocked polyisocyanate compound, for example, a blocking product of dipheylmethanediisocyanate with caprolactam, in a solid weight ratio of 1/10 to 1/3, more preferably about 1/5, to the solid weight of the rubber latex (L). The blocked polyisocyanate compound contributes to enhancing the adhesive performance of the resultant adhesive-treated polyester fiber cord.
The method of applying the second adhesive liquid is not limited to a specific method. Usually, an immersion method is employed. Preferably, the dry amount of the effective components of the second adhesive liquid applied to the first adhesive-treated polyester fiber cord is controlled to 2.0 to 3.0% by weight, more preferably 2.2 to 2.8% by weight, based on the weight of the polyester fiber cord.
The second adhesive liquid applied cord is preferably dried at a temperature of 150 to 180xc2x0 C. for 90 to 150 seconds under such a condition that the cord is not slackened, and then heat-treated at a temperature of 180 to 240xc2x0 C., more preferably 210 to 240xc2x0 C. for 60 to 180 seconds, more preferably 90 to 150 seconds. The heat treatment for the second adhesive liquid-applied polyester fiber cord is preferably carried out under a relaxed condition such that the cord is allowed to shrink at a shrinkage of 0.5 to 1.5, more preferably about 1.0%.
In an embodiment of the process of the present invention, the second adhesive-treated polyester fiber cord is subjected to a third adhesive-treating procedure in which a third adhesive liquid comprising an aqueous dispersion of a resorcinol-formaldehyde condensation product component (RF) in a molar ratio (R/F) of resorcinol (R) to formaldehyde (F) of 1/0.6 to 1/1.0 and a rubber component (G) containing at least natural rubber (NR) in a content of at least 15% by weight based on the total weight of the rubber component (G), in a solid weight ratio (RF/G) of the resorcinol-formaldehyde condensation product component (RF) to the rubber component (G) of 1/10 to 1/20, is applied to the second adhesive-treated polyester fiber cord, and the third adhesive liquid-applied polyester fiber cord is heat-treated at a temperature of 140 to 170xc2x0 C.
In third adhesive liquid, the molar ratio (R/F) of resorcinol (R) to formaldehyde (F) of the resorcinol-formaldehyde condensation product component (RF) is controlled to 1/0.6 to 1/1, preferably 1/0.7 to 1/0.9, for the purpose of allowing the resultant third adhesive coating on the cord to be slightly three-dimensionally cross-linked to enhance the adhesive property of the cord itself and to improve the adhesion of the resultant cord to a non-vulcanized rubber in a product forming procedure without reducing the bonding property of the third adhesive coating.
For the same purpose as mentioned above, the solid weight ratio (RF/G) of the resorcinol-formaldehyde condensation product component (RF) to the rubber component (G) is controlled to 1/10 to 1/20, preferably 1/12 to 1/18. The resorcinol-formaldehyde condensation product component (RF) and the rubber component (G) are employed in the state of an aqueous dispersion. The rubber component (G) comprises at least natural rubber (NR). When an aqueous dispersion of the rubber component (G) or the natural rubber (NR), is used, preferably, the aqueous dispersion is prepared by dispersing the rubber component in water without using a dispersing agent. Even when the dispersing agent is used, the content of the dispersing agent is preferably restricted to less than 5% by weight, based on the dry weight of the natural rubber.
There is no limitation to the method of applying the third adhesive liquid to the second adhesive-applied polyester fiber cord. Usually an immersion method is utilized. The amount of the effective components of the third adhesive liquid applied to the cord is preferably controlled to 0.5 to 1.5%, more preferably 0.8 to 1.3% by dry solid weight, based on the dry weight of the polyester fiber cord.
In the process of the present invention, the third adhesive liquid-applied polyester fiber cord must be heat-treated at a temperature lower than the heat treatment temperatures for the first adhesive liquid-applied cord and the second adhesive liquid-applied cord, namely, of 140 to 170xc2x0 C., preferably 145 to 165xc2x0 C., for 120 to 240 seconds, preferably 150 to 200 seconds, to semi-cure the third adhesive coating on the cord. This heat treatment contributes to enhancing the adhesion of the resultant third adhesive coating to the non-vulcanized rubber and to preventing the separation of the cord when the cord is employed to form a rubber composite product, for example, a belt. Also, the third adhesive coating exhibits excellent compatibility with both the second adhesive coating formed from the second adhesive liquid and the matrix rubber used for the rubber composite product, and can be sufficiently cross-linked and cured by the vulcanizing procedure for the rubber composite product, for example, a belt, and thus the resultant cord can exhibit an excellent adhesive performance. Further, even when the adhesive-treated polyester fiber cord produced by the process of the present invention is undesirably exposed to water vapor, no reduction in adhesive performance occurs.
The third adhesive liquid optionally contains an aqueous dispersion of carbon black (C) produced by a conventional method, in an effective component weight ratio (C/(RF+G)) of the carbon black (C) to the total of the resorcinol-formaldehyde condensation product component (RF) and the rubber component (G) of 1/3 to 1/10, preferably 1/4 to 1/8. The carbon black (C) added to the third adhesive liquid covers the peripheral surface of the resultant adhesive-treated polyester fiber cord and contributes to enhancing the resistance of the cord to ultraviolet rays, and to preventing a reduction in the adhesive performance of the cord.
In another embodiment of the process of the present invention, the third adhesion procedure for the second adhesive-treated polyester fiber cord is carried out by using a third adhesive liquid comprising an aqueous dispersion of a resorcinol-formaldehyde condensation product component (RF) in a molar ratio (R/F) of resorcinol (R) to formaldehyde (F) of 1/0.6 to 1/1.0 and a rubber component (G) containing natural rubber (NR) and a vinylpyridine-styrene-butadiene copolymer rubber (VpR) in a solid weight ratio (NR/VpR) of 2/8 to 4/6, in a solid weight ratio (RF/G) of the resorcinol-formaldehyde condensation product component (RF) to the rubber component (G) of 1/10 to 1/20, and the third adhesive liquid-applied polyester fiber cord is heat-treated at a temperature of 140 to 170xc2x0 C.
In the rubber component (G) for the third adhesive liquid, the natural rubber (NR) and the vinyl pyridine-styrene-butadiene copolymer rubber (VpR) are mixed with each other in a solid weight ratio (NR/VpR) of 2/8 to 4/6, preferably 3/7 to 7/13. When the ratio (NR/VpR) is more than 2/8, while the adhesion of the resultant adhesive-treated cord to the non-vulcanized rubber is enhanced, the resultant cord exhibits too high a stickiness to other cords and thus the handling property of the cords is degraded. When the ratio (NR/VpR) is less than 4/6, the adhesion of the resultant cord to the non-vulcanized rubber is reduced.
In the resorcinol-formaldehyde condensation product component (RF) for the third adhesive liquid, the molar ratio (R/F) of resorcinol (R) to formaldehyde (F) is 1/0.6 to 1/1.0, preferably 1/0.7 to 1/0.9.
The specific molar ratio (R/F) as mentioned above contributes to enabling the resultant third adhesive coating to be slightly three-dimensionally cross-linked with the resorcinol-formaldehyde condensation product component (RF), and to enhancing the adhesive property of the resultant cord so as to increase the adhesion of the resultant cord to the non-vulcanized rubber in the forming procedure without decreasing the bonding property of the third adhesive coating. For the same purpose as mentioned above, the solid weight ratio (RF/G) of the resorcinol-formaldehyde condensation product component (RF) to the rubber component (G) comprising the natural rubber (N/R) and the vinyl pyridine-styrene-butadiene copolymer rubber (vpR) is controlled to 1/10 to 1/20, preferably 1/12 to 1/18. The aqueous dispersion of the natural rubber (NR) is preferably prepared by not using a surface active agent. Even when the surface active agent is used, the content of the surface active agent should be restricted to less than 5% by weight based on the dry weight of the natural rubber.
There is no limitation to the method of applying the third adhesive liquid to the second adhesive-applied polyester fiber cord. Usually an immersion method is utilized. The amount of the effective components of the third adhesive liquid applied to the cord is preferably controlled to 0.5 to 1.5%, more preferably 0.6 to 1.3% by dry solid weight, based on the dry weight of the polyester fiber cord.
In the embodiment of the process of the present invention, the third adhesive liquid-applied polyester fiber cord must be heat-treated at a temperature lower than the heat treatment temperatures for the first adhesive liquid-applied cord and the second adhesive liquid-applied cord, namely, of 140 to 170xc2x0 C., preferably 150 to 165xc2x0 C., for 120 to 240 seconds, preferably 150 to 200 seconds, to semi-cure the third adhesive coating on the cord. This heat treatment contributes to enhancing the adhesion of the resultant third adhesive coating to the non-vulcanized rubber and to preventing the separation of the cord when the cord is employed to form a rubber composite product, for example, a belt. Also, the third adhesive coating exhibits excellent compatibility with both the second adhesive coating formed from the second adhesive liquid and the matrix rubber used for the rubber composite product, and can be sufficiently cross-linked and cured by the vulcanizing procedure for the rubber composite product, for example, a belt, and thus the resultant cord can exhibit an excellent adhesive performance. Further, even when the adhesive-treated polyester fiber cord produced by the process of the present invention is undesirably exposed to water vapor, no reduction in adhesive performance occurs.